Docs: Add a section for custom file extension

docs/content/usage/scenarios/ransomware-simulation.md

@@ -37,15 +37,21 @@ To ensure minimum interference and easy recoverability, the ransomware
 simulation will only encrypt files contained in a user-specified directory. If
 no directory is specified, no files will be encrypted.
 
+Infection Monkey appends the `.m0nk3y` file extension to files that it
+encrypts. You may optionally provide a custom file extension for Infection
+Monkey to use instead. You can even provide no file extension, but take
+caution: you'll no longer be able to tell if the file has been encrypted based
+on the filename alone!
+
 ![Ransomware configuration](/images/usage/scenarios/ransomware-config.png "Ransomware configuration")
 
 ### How are the files encrypted?
 
 Files are "encrypted" in place with a simple bit flip. Encrypted files are
-renamed to have `.m0nk3y` appended to their names. This is a safe way to
-simulate encryption since it is easy to "decrypt" your files. You can simply
-perform a bit flip on the files again and rename them to remove the appended
-`.m0nk3y` extension.
+renamed to have a file extension (`.m0nk3y` by default) appended to their
+names. This is a safe way to simulate encryption since it is easy to "decrypt"
+your files. You can simply perform a bit flip on the files again and rename
+them to remove the appended `.m0nk3y` extension.
 
 Flipping a file's bits is sufficient to simulate the encryption behavior of
 ransomware, as the data in your files has been manipulated (leaving them